In recent years, a push switch which needs a long stroke has been preferred as an operating section of electronic devices, e.g. a car air-conditioner, car audio device, and other audio-visual devices, because those devices need lighting and a higher density at their operating panels.
Such a conventional push switch as discussed above is described hereinafter with reference to FIG. 8 and FIG. 9. FIG. 8 shows an exploded perspective view of the conventional push switch, and FIG. 9 shows a sectional view cut along line 9-9 in FIG. 8. Box-shaped housing 1 shown in FIG. 8 is open at its top and made of insulating resin, and its recessed section forms typically a cubic space. A pair of fixed contacts 2 is rigidly mounted to the center of the inner bottom face of the recessed section. Fixed contacts 2 are made of well-conductive metal plate and stay bared by insert-molding. Each one of fixed contacts 2 extends outward from the side wall of housing 1, and each one of the extended tips forms terminal 7.
Resilient unit 3 is shaped like a cone open at its bottom and made of silicone rubber. It is placed on the inner bottom face of housing 1, and includes well-conductive movable contact 4 placed on the underside of the ceiling within the cone shape. The lower perimeter of resilient unit 3 is positioned by retainers 1A provided at lower sections on the inner wall of housing 1.
Operating unit 5 made of insulating resin is formed of square-shaped plane section 5A, legs 5B depending from each one of the four corners of plane section 5A, and projections 5C projecting laterally from the lower end of legs 5B. Plane section 5A is seated on a flat top face of resilient unit 3.
Cover 6 made of thin metal plate includes rectangular hole 6A at its center, and is mounted to housing 1 such that plane section 5A of operating unit 5 protrudes from rectangular hole 6A. The top opening of housing 1 is covered with a flat portion around rectangular hole 6A.
Each one of legs 5B of operating unit 5 is placed correspondingly to each one of the four corners of the recessed section of housing 1. Each one of the four corners forms guide bore 1B which is formed by inner faces of adjacent two walls of housing 1 and lateral walls of each one of retainers 1A. When operating unit 5 moves downward, projection 5C projected from the lower end of leg 5B is guided along guide bore 1B.
Plane section 5A of operating unit 5 of the push switch discussed above is depressed, then projection 5C of leg 5B lowers along guide bore 1B provided at the inside corner of housing 1 while the perimeter of plane section 5A is regulated by rectangular hole 6A. This lowering prompts plane section 5A to push resilient unit 3 downward, and when operating unit 5 is depressed by a given stroke, a flaring section forming the cone shape of resilient unit 3 is deformed resiliently with tactile feeling, so that movable contact 4 placed on the underside of the ceiling within resilient unit 3 is brought into contact with the pair of fixed contacts 2, namely, the push switch is turned ON.
A removal of depressing force from operating unit 5 prompts the flaring section, deformed resiliently, of resilient unit 3 to restore itself to its original position due to its own restoring force. Operating unit 5 is thus pushed back and movable contact 4 leaves fixed contacts 2, and the push switch returns to OFF status again. At this time operating unit 5 returns to its original position as shown in FIG. 9 with its foregoing respective sections being regulated.
Related art to the present invention is disclosed in, e.g. Japanese Utility Model Unexamined Publication No. H04-111119.
Since the conventional push switch discussed above meets a long stroke requirement and is excellent in operation, it has been used in a large number of devices. However, this conventional push switch has often invited requirements of downsizing and a slimmer body because of the market trend in which downsizing of the devices has been in progress and a higher density of mounting the components also has been in progress. During the operation of this push switch, its projection 5C projecting laterally from the lower end of leg 5B moves along guide bore 1B while the perimeter of plane section 5A, i.e. an upper part of operating unit 5, is regulated by rectangular hole 6A of cover 6. Since operating unit 5 moves up and down in the foregoing mechanism, given clearances are needed between the respective elements.
The climate of favoring the downsizing of the devices makes it difficult to greatly reduce the foregoing clearances necessary for maintaining the smooth up and down movement of operating unit 5. In particular, an employment of a downsized structure and a slimmer body with the conventional structure maintained will produce a difference in distances between the center and peripherals of operating unit 5 supported by resilient unit 3. When operating unit 5 is depressed at a place slightly shifted along the longitudinal direction due to an error produced by a combination of operating buttons with each other, the short side nearer to the shifted depression place tends to move downward, i.e. the short side tends to be jammed, which needs to be overcome.